Cell C over charging me

Since December 2014 when i did upgrades on my contracts with Cell C i have been fighting a losing battle. From the start i asked for limits on my accounts but not one single month have i paid the amount it should be. It start with me being informed by Cell C that i have got open lines with them up to R15 000 per month per contract. The latest is that when i called today, the consultant at Cell C hang up the phone in my ear when i refused to tell what my last payment was, which was regardless to my query. I have also requested Cell C Witteklip Mall for some information(Janice is her name)but i am still waiting. Every month i am paying between R1300-R1800 for contracts that is suppose not to cost me more than say R750-R800. How the hell is this possible??